//鍵盤代理事件
- (void)keyboardWillHide:(NSNotification *)notification{
    _keyBoardShowIng = NO;
    [UIView animateWithDuration:.25 animations:^{
        downView.top = MainScreenHeight;
        if (_richTextToolBar) {
            dispatch_async(dispatch_get_main_queue(), ^{
                 _richTextToolBar.hidden = YES;
            });
           
        }
    }];
    
}

- (void)keyboardWillShow:(NSNotification *)notification{
    _keyBoardShowIng = YES;
     NSDictionary *userInfo = [notification userInfo];
     NSValue * endValue   = [notification.userInfo objectForKey:UIKeyboardFrameEndUserInfoKey];
     CGFloat height = [endValue CGRectValue].size.height;
     if(height==0) return;

    
    NSNumber *duration = [userInfo objectForKey:UIKeyboardAnimationDurationUserInfoKey];
    
    NSNumber *curve = [userInfo objectForKey:UIKeyboardAnimationCurveUserInfoKey];
    
    // 添加移動(dòng)動(dòng)畫，使視圖跟隨鍵盤移動(dòng)
    
    [UIView animateWithDuration:duration.doubleValue animations:^{
        
        [UIView setAnimationBeginsFromCurrentState:YES];
        
        [UIView setAnimationCurve:[curve intValue]];
        
        downView.bottom = MainScreenHeight - height;
        
    }];
}

但是記得下面

-(void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
    
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillShowNotification object:nil];
     [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillHideNotification object:nil];

}

-(void)viewWillAppear:(BOOL)animated{
    [super viewWillAppear:animated];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];

}